The present invention relates to a display tube for a light source that utilizes light emission of a phosphor and a method of manufacturing the same and, more particularly, to a display tube for a light source that constitutes pixels in, e.g., a color display unit having a large screen and a method of manufacturing the same.
FIGS. 6A and 6B explain the arrangement of a conventional fluorescent display tube for a light source, in which FIG. 6A shows this display tube as a whole, and FIG. 6B shows a portion B of FIG. 6A. Referring to FIGS. 6A and 6B, reference numeral 1 denotes a cylindrical glass bulb; and 2, a face glass sealed at one open end of the glass bulb 1 through a frit glass seal 3. The glass bulb 1, the face glass 2, and the frit glass seal 3 constitute a cylindrical glass bulb assembly 4 having one sealed end. Reference numeral 5 denotes a phosphor screen adhered on the rear side of the face glass 2; 6, an Al metallized film formed on the phosphor screen 5; 7, an anode formed on the inner wall surface of the glass bulb 1 on the face glass 2 side and made of a carbon film; and 8, a Ba gettered film formed between the Al metallized film 6 and the anode 7 for electrically connecting them.
A stem assembly 20 is bonded to the other open end of the glass bulb assembly 4. A stem glass 21 is sealed at the other open end of the glass bulb 1 through a frit glass seal 22. An exhaust pipe 23 is integrally formed with the stem glass 21. A cylindrical anode electrode 24 is fixed to the distal end portion of an anode lead 26 connected to a lead pin 25a extending through the stem glass 21. A bulb spacer contact 27 is mounted and fixed to the distal end portion of the anode electrode 24 and is brought into contact with the anode 7 to be electrically connected to it. A Ba getter 28 is mounted and fixed to the distal end portion of the bulb spacer contact 27. A cathode assembly 29 is fixed to the distal end portions of cathode leads 30 connected to lead pins 25b extending through the stem glass 21. In the cathode assembly 29, a back plate 32 and a filament cathode 33 are mounted on a ceramic plate 31. The back plate 32, the filament cathode 33, and the ceramic plate 31 are surrounded by a grid housing 34 having a mesh portion 34a at its central portion, thereby forming the cathode assembly 29.
In the display tube for a light source having the above arrangement, a high voltage applied from an external circuit to the lead pin 25a flows along a path of the anode lead 26.fwdarw.the anode electrode 24.fwdarw.the bulb spacer contact 27.fwdarw.the anode 7.fwdarw.the Ba gettered film 8 and is applied to the Al metallized film 6. Electron beams emitted from the cathode assembly 29 upon application of the voltage from the external circuit to the lead pins 25b are radiated to the phosphor screen 5 to excite it. Emission colors corresponding to the phosphors are displayed on the front surface side through the face glass 2.
However, the display tube for a light source having the above arrangement has problems as follows.
(1) Since the frit glass seal 3 is used to bond the face glass 2 and the glass bulb 1, the adhesion area is only the end portions of the glass members, thus decreasing the adhesion strength. In a heat test, the glass plate tends to be separated from this portion.
(2) The Al metallized film 6 adhered on the rear surface side of the phosphor screen 5 formed on the face glass 2 and the carbon anode 7 formed on the inner surface of the glass bulb 1 are brought into contact with each other through the Ba gettered film 8. The conductivity of the Ba gettered film 8 largely changes due to the gas emission amount in the pipe and the film quality (the film thickness and the gas adsorbing state). As the time passes in use, defective conduction caused by an increased resistance tends to occur, resulting in poor reliability in electrical connection.
(3) A carbon printed layer (coating layer) exists as the anode 7 on the inner surface of the glass bulb 1. Sometimes the carbon printed layer emits gas or the carbon powder falls to interfere with application of a high voltage.
(4) Since the frit glass seal 22 identical to that used in the above item (1) is used to bond the glass bulb 1 and the stem assembly 20, the adhesion strength is insufficient and heat resistance is low. Abnormal electric discharge sometimes occurs at the high-voltage applying pin portion, resulting in poor reliability.
(5) Since the front surface side of the face glass 2 is formed flat, emitted light does not spread largely, thereby greatly limiting the angle of visual field.